Quote from KyoShinda
Those tweaks make minimal differences. If you get surrounded by a bunch of good-AI zombies that can bust down doors, they'll still do the same damage to your easily-obtainable iron set. Do you see my point yet?
My point is, zombies shouldn't be tweaked.
Difficulty isn't just how strong mobs are, it's multiple factors.
The biggest flaw right now, being how fast you are able to reach that point where zombies aren't a threat, it needs to be cut down a lot.
So, cutting down on iron ores helps, and so does adding a new set of mobs that are buffed, or stronger, or ect.
As difficulty isn't about adding a mob that has more HP and stronger hits, but also a mob that has abilities, such as flying..
Understand my point?
Torches/Lanterns just delay the steps between say, iron and diamond. Even if only slightly.
And, the other one will make overall more mobs spawn throughout the world. Not much more challenging, but more encounters of mobs does add challenge.